1. Field of the Invention
The present invention relates to an improvement in a very high frequency television tuner. More specifically, the present invention relates to an improvement in an adjusting scheme of an intermediate frequency transformer provided in a very high frequency tuner, particularly for use in a television receiver.
2. Description of the Prior Art
Of late, some types of very high frequency (hereinafter referred to as VHF) television receivers have been designed in accordance with the recent trend of miniturization and economy of materials. Such types of VHF television receivers often require that a VHF tuner be installed close to the inside of a cabinet of a television receiver or close to other circuit components. Typically, such a television tuner includes: a mechanical switching selection scheme of inductance coil means for selection of a broadcasting television signal; a radio frequency amplifier operatively coupled to said inductance coil means for selectively amplifying a desired radio frequency signal; a local oscillator operatively coupled to said inductance coil means for providing a local oscillation frequency signal, the frequency of which is different by a given frequency difference from said selectively amplified radio frequency signal; a mixer responsive to the selectively amplified radio frequency signal from the radio frequency amplifier and the local oscillation frequency signal from the local oscillator for providing an intermediate frequency signal; and an intermediate frequency tuned circuit for selectively withdrawing the said intermediate frequency signal.
The above mentioned mechanical switching selection scheme of inductance coil means may comprise a so-called turret type structure, i.e. a plurality of sets of coils, each set allotted for one channel, provided on a turret rotatably mounted so as to be rotated by means of a channel selection shaft, and a switching contact arrangement for selection of a desired set of coils as a function of manual rotation of the channel selection shaft. Alternatively, the above described mechanical switching selection scheme of inductance coil means may comprise a so-called switch type structure, i.e., a plurality of sets of coils, each set allotted for one channel, provided in a stationary manner along the periphery around a given axis, and a switching contact arrangement rotatably mounted about the axis so as to be rotated by means of a channel selection shaft.
Such a very high frequency television tuner for selection of a broadcasting television signal through mechanical switching selection of inductance coil means is usually mounted in a television receiver cabinet such that the end of a channel selection shaft comes outside the control panel of the cabinet and a channel selection knob is mounted to the end of the channel selection shaft for facility of manual rotation of the shaft. Thus, it would be appreciated that the position and orientation of the tuner installed in the television receiver cabinet are somewhat limitative.
On the other hand, the above described intermediate frequency tuned circuit typically comprises an intermediate frequency transformer and a capacitor connected across the transformer. As is well known to those skilled in the art, such an intermediate frequency transformer requires adjustment of the inductance value thereof. Typically, a conventional intermediate frequency transformer comprises an inductance coil wound on a bobbin which comprises a magnetic core threadably mounted in the bobbin for allowing to and fro movement of the magnetic core in the axial direction by rotating the magnetic core about the axis of the bobbin by means of a special purpose tool such as a screw driver, whereby adjustment of the inductance value of the intermediate frequency transformer is achieved by simply turning the magnetic core about the axis with a screw driver inserted into the bobbin so as to be engaged with the magnetic core and to adjustably position the core in the axial direction of the bobbin.
FIGS. 1 and 2 are illustrative of two examples of a simplified side view of a typical conventional VHF television tuner 1 for the purpose of showing the arrangement of the first stage intermediate frequency transformer 2 inside the television tuner 1. Typically, the turner 1 comprises a channel selection shaft 3 rotatably mounted and extending in the longitudinal direction of the tuner 1. Thus, the tuner 1 is usually positioned and oriented in the television receiver cabinet 4 such that the channel selection shaft 3 extends in the horizontal direction and the end of the shaft 3 comes outside of the cabinet 4 through an aperture 6, the end of the shaft 3 being then connected to a channel selection knob 5.
In such a conventional VHF television tuner, no consideration has been given to the orientation of the intermediate frequency transformer 2 from the standpoint of the adjustment of the inductance value of the transformer. More specifically, as seen in such a conventional VHF television tuner shown in FIGS. 1 and 2, the intermediate frequency transformer 2 has been oriented only from the standpoint of simplicity of structure for fixing the transformer to the tuner casing, such that the axis of the bobbin of the intermediate frequency transformer 2 extends in the vertical direction or substantially in the vertical direction when the tuner 1 is provided in the television receiver cabinet 4, most typically with the channel selection shaft 3 extending in the horizontal direction. The reason for this is presumably that the intermediate frequency transformer 2 is mounted simply by fixing, at a right angle or substantially at a right angle, the bobbin of the transformer to the circuit board or the tuner casing of the tuner which extends in the same direction as the channel selection shaft 3. Therefore, in such an orientation of the intermediate frequency transformer 2, it becomes difficult or impossible, as the case may be, to adjust the inductance value of the intermediate frequency transformer once the tuner is installed in the television receiver cabinet, adjustment being hindered by the cabinet wall or the other circuit components. Another problem encountered in a conventional VHF television tuner is that, since a tuner is installed in a television receiver cabinet after adjustment of various circuit components, including an intermediate frequency transformer, it could happen that these components will be brought to a misadjusted state because of an adverse affect of the cabinet upon these components, and the adjustment of these components is again difficult for the above described reason.